(1) Field of the Invention
This invention relates to compressors, and more particularly to screw-type compressors.
(2) Description of the Related Art
Screw-type compressors are commonly used in refrigeration applications. In such a compressor, intermeshed male and female lobed rotors or screws are driven about their axes to pump the refrigerant from a low pressure inlet end to a high pressure outlet end. In one implementation, the male rotor is coaxial with an electric driving motor and is supported by bearings on inlet and outlet sides of its lobed working portion. An exemplary inlet side bearing is a roller bearing. Such bearings require oil for lubrication. If not prevented from doing so, such oil may exit the bearing cavity and become entrained in refrigerant as it passes downstream through the compressor. For some applications this is not advantageous. There may be a tendency for oil to accumulate in the evaporator of the refrigeration system. A reclamation system may be provided to return this oil to the compressor.
Various shaft seal arrangements have been used to hinder the leakage of oil from bearing cavities. A shaft seal arrangement that is well known in the general art of compressor design is the buffered labyrinth seal. In such a seal, a flow of gas at moderate or high pressure is introduced into a buffer volume interposed between two sets of annular teeth that are in close-running proximity to the rotor shaft. The gas flow raises the pressure of the buffer volume above the pressure in the bearing cavity, thereby causing gas flow into the bearing cavity to prevent the flow of oil out of the bearing cavity. The annular teeth act as flow restrictions which allow for development of higher pressure in the buffer volume without requiring an excessive gas flow rate.